1. Field of the Present Invention
The present invention relates to an image forming apparatus such as printer, facsimile machine, Photocopier or MFP (Multi-Function Product) with more than two functions.
2. Related Background Art
Conventionally, image forming apparatus used in an electro photographic system charges the surface of the photosensitive drum evenly, then forms an electrostatic latent image on surface of photosensitive drum through an exposure apparatus, and then develops the electrostatic latent image on the photosensitive drum to form a toner image, finally transfers the toner image on paper through a development apparatus.
In the conventional image forming apparatus, a density of image is usually determined by a quantity of toner transferred on the paper. Nevertheless, because of such factors as the change of operating environment and frequency, there existed circumstances of change in image density. Therefore many methods aimed at prohibiting the change of image density and adjusting the image density into a target level are put forward.
For example: to charge the photosensitive drum under predetermined charge voltage circumstances, to expose with predetermined exposure quantity and to form the electrostatic latent image, to develop the toner into the electrostatic latent image with predetermined development bias voltage, and then to form the test pattern on the photosensitive drum and transfer belt and to detect the density of the test pattern through toner density detecting section. To compare the detected value with standard value, then to control the image forming circumstances such as, light quantity of exposure apparatus, development bias voltage and toner providing bias voltage, and finally to form the image density at target level on the paper.
Patent document 1 (Japanese patent publication 11-184190).
Nevertheless, with the image forming apparatus referred above, there used to exist a problem that image fog is deteriorating (non-image part is tainted).